This invention relates to a system for the cleaning of equipment used in the production of semiconductor devices. In particular, this invention relates to an apparatus for the cleaning of low pressure chemical vapor deposition chambers utilizing r.f. techniques.
A known process in the manufacture of semiconductors utilizes low pressure chemical vapor deposition. This technique is used in the formation of layers such as silicon nitride, silicon dioxide and polysilicon on a silicon substrate. Low pressure techniques, that is, in the range of 0.5-3 torr have advantages in terms of uniformity in processing especially for passivation. Typically, the substrate is placed in a reaction chamber which is heated and brought to a low pressure state. A reaction gas is introduced into the chamber such that the reaction material is deposited on the semiconductor substrate either by reaction or thermal decomposition of the reaction gas.
While offering advantages in terms of a system through-put and high product level quality, low pressure chemical vapor deposition results in the buildup of deposition products on the walls of the reaction chamber. The chamber is typically a quartz tube. Unless periodically cleaned, this buildup results in flakes which tend to contaminate the semiconductor products and cause defects in the layers being formed. Consequently, unless the reaction material deposited on the inner walls of the reaction chamber is removed, it may contaminate the substrate during processing so that normal growth and coating cannot occur.
It is therefore necessary to periodically clean the reaction chamber to remove these undesired deposits. Within the technology such contaminants are currently removed by wet etching the quartz tube in a solution of hydrofluoric and nitric acid. This wet etch process requires that the apparatus be completely broken down and the quartz tube removed. Thus, the equipment is unusable for a period of time up to 24 hours.
Other techniques have been proposed such as heating the reaction chamber to a high temperature, for example 1000.degree. C. and then introducing the same type of corrosive gas into the reaction chamber. This technique, however, requires high temperatures and cannot be used on those materials which cannot be subjected to such a temperature regime.
Within the prior art, other techniques are known for the treatment of semiconductors and/or associated reaction equipment. For example, in the case of plasma enhanced C.V.D. systems, etch cleaning of the chambers is accomplished simply by introducing a cleaning gas into the chamber environment. Such a system is shown in U.S. Pat. No. 4,138,306. Cleaning plasma is generated externally and introduced into the reaction chamber 1 by means of a conduit 7. A plasma generating section 9 utilizes microwave energy, oscillator 11 supplied via a wave guide 12 such that the microwaves activate the etching gas which is then introduced into the reaction chamber. Such a system while offering advantages of simplicity in terms of the cleaning steps per se results in a complicated and expensive device. In essence, a dedicated microwave system is required for activating of the cleaning gas.
U.S. Pat. No. 3,924,024 relates to a technique of treating the oxide surface of wafers prior to deposition of silicon nitride. Other patents dealing specifically with the cleaning or etching of wafers utilizing activated gas reaction components are identified in U.S. Pat. Nos. 4,065,369 and 4,278,493. These systems relate to the cleaning or etching of wafers and not to reaction of chambers and deposition C.V.D. equipment itself. Other prior art directed to the cleaning or etching of wafers is shown in U.S. Pat. Nos. 4,088,926 and 4,278,493. These prior art systems relate to the cleaning of wafer surfaces utilizing ion milling and the like. Other patents considered but deemed to be of less interest are U.S. Pat. Nos. 4,058,638 and 4,220,116. These patents deal respectively with techniques for performing multiple semiconductor manufacture operations in a common chamber or to a gas flow structure utilized in low pressure chemical vapor deposition systems to create uniform films. Neither of the patents deal specifically with the concepts or problems of cleaning the system.